Re: [Resend][Bug fix PATCH v5] Reusing a resource structure allocatedby bootmem

[Yasuaki Ishimatsu]

2013/04/25 5:37, Andrew Morton wrote:
> On Wed, 24 Apr 2013 08:50:21 +0900 Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> wrote:
>
> > When hot removing memory presented at boot time, following messages are shown:
> >
> > [  296.867031] ------------[ cut here ]------------
> > [  296.922273] kernel BUG at mm/slub.c:3409!
> >
> > ...
> >
> > The reason why the messages are shown is to release a resource structure,
> > allocated by bootmem, by kfree(). So when we release a resource structure,
> > we should check whether it is allocated by bootmem or not.
> >
> > But even if we know a resource structure is allocated by bootmem, we cannot
> > release it since SLxB cannot treat it. So for reusing a resource structure,
> > this patch remembers it by using bootmem_resource as follows:
> >
> > When releasing a resource structure by free_resource(), free_resource() checks
> > whether the resource structure is allocated by bootmem or not. If it is
> > allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
> > not allocated by bootmem, free_resource() release it by kfree().
> >
> > And when getting a new resource structure by get_resource(), get_resource()
> > checks whether bootmem_resource has released resource structures or not. If
> > there is a released resource structure, get_resource() returns it. If there is
> > not a releaed resource structure, get_resource() returns new resource structure
> > allocated by kzalloc().
> >
> > ...
>
> Looks good to me.
>
> > --- a/kernel/resource.c
> > +++ b/kernel/resource.c
> > @@ -21,6 +21,7 @@
> >   #include <linux/seq_file.h>
> >   #include <linux/device.h>
> >   #include <linux/pfn.h>
> > +#include <linux/mm.h>
> >   #include <asm/io.h>
> >
> >
> > @@ -50,6 +51,14 @@ struct resource_constraint {
> >
> >   static DEFINE_RWLOCK(resource_lock);
> >
> > +/*
> > + * For memory hotplug, there is no way to free resource entries allocated
> > + * by boot mem after the system is up. So for reusing the resource entry
> > + * we need to remember the resource.
> > + */
> > +static struct resource *bootmem_resource_free;
> > +static DEFINE_SPINLOCK(bootmem_resource_lock);
> > +
> >   static void *r_next(struct seq_file *m, void *v, loff_t *pos)
> >   {
> >   	struct resource *p = v;
> > @@ -151,6 +160,40 @@ __initcall(ioresources_init);
> >
> >   #endif /* CONFIG_PROC_FS */
> >
> > +static void free_resource(struct resource *res)
> > +{
> > +	if (!res)
> > +		return;
> > +
> > +	if (!PageSlab(virt_to_head_page(res))) {
>
> Did you consider using a bit in resource.flags?  There appear to be
> four free ones left.  The VM trickery will work OK I guess, but isn't
> very "nice".
>
> > +		spin_lock(&bootmem_resource_lock);
> > +		res->sibling = bootmem_resource_free;
> > +		bootmem_resource_free = res;
> > +		spin_unlock(&bootmem_resource_lock);
> > +	} else {
> > +		kfree(res);
> > +	}
> > +}
> > +
> > +static struct resource *get_resource(gfp_t flags)
> > +{
> > +	struct resource *res = NULL;
> > +
> > +	spin_lock(&bootmem_resource_lock);
> > +	if (bootmem_resource_free) {
> > +		res = bootmem_resource_free;
> > +		bootmem_resource_free = res->sibling;
> > +	}
> > +	spin_unlock(&bootmem_resource_lock);
> > +
> > +	if (res)
> > +		memset(res, 0, sizeof(struct resource));
> > +	else
> > +		res = kzalloc(sizeof(struct resource), flags);
> > +
> > +	return res;
> > +}

> I think I'll rename this to alloc_resource().  In Linux "get" often
> (but not always) means "take a reference on".  So "get" pairs with
> "put" and "alloc" pairs with "free".

I forgot to answer it.
I think so too. And I have no objection about your update patch.

Thanks,
Yasuaki Ishimatsu

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